1. Field of the Invention
The present invention relates to a telephone ringer and more particularly to a telephone ringer wherein the clapper is a magnetically controlled steel ball freely mounted to be driven against a gong. The ball is magnetically biased to provide polarity independent bell tap suppression.
2. Description of the Prior Art
Heretofore telephone ringers have been provided as assemblies including one or two gongs, a clapper mounted on the end of a pivotably mounted clapper arm, and an electromagnet for driving the clapper. Typical ringers are shown in U.S. Pat. Nos. 2,590,500; 2,692,380; and 4,054,870. Characteristically the clappers have a significant mass and the arms are of considerable length. Due to the lever arm effect a rather large and powerful electromagnet was required. Accordingly, the ringers are inherently large, complex mechanical assemblies having excessive weight. The cost of the required components and the labor intensive assembly contributed significantly to the expense of a telephone subset. A need existed in the art for a smaller and less expensive telephone ringer.
A mechanically simple, but large and heavy electromagnetic signaling instrument, developed by S. H. Sauve is shown in U.S. Pat. No. 1,009,345. FIG. 5 of the patent shows a double gong ringing device having a ball armature mounted in an opening formed in a permanent magnet disposed between two gongs. A pair of coils are energized so that the ball vibrates between the two gongs. The patent does not disclose how the coils are energized; however, it is presumed that using modern technology an AC signal would be used. For unknown reasons the Suave device was never improved for use in modern telephony.
A problem that has consistently plagued the designers of telephone ringers is that of bell tap or false ring. False ring occurs when multiple subsets are connected to the same line pair and one subset is dialed. The dial pulses generated by one subset inadvertently pass to the ringer of another subset causing a false ringing of the other subset.
Telephone ringers are connected in parallel with the telephone subset to a line pair. A capacitor is connected in series with the ringer to block DC current while freely passing an AC ringing signal. Ringers must be adjusted to have sufficient sensitivity to operate at frequencies between 20 and 30 Hz with minimum voltages of 45 volts RMS at 20 Hz and 65 volts RMS at 30 Hz. Thus, the ringer must have a prescribed minimum sensitivity.
Dial pulses generate unipolar voltage spikes up to approximately 470 volts. These voltage spikes pass through the blocking capacitor of the ringer and cause the clapper arm to move in one direction resulting in bell tap. In order to overcome the difficulty of bell tap, most modern ringers provide a bias spring on the clapper arm to restrain the movement of the arm in the direction that would result from the unipolar dial pulse spikes.
While the above solution for bell tap has been moderately successful, recent changes in the telephone industry have resulted in a new rash of bell tap complaints. Many consumers are now buying and installing their own telephone subsets. Installing a telephone subset requires the connection of two wires, a red and a green wire, to the line pair. If these wires are not connected properly, bell tap will not only occur, but will be acerbated by the fact that the bias spring urges the arm in the direction of motion caused by the dial pulses. Thus, the use of a bias spring is no longer a satisfactory solution to the bell tap problem.
The Sauve patent did not address the bell tap problem because dial type systems had not yet been invented at the time of the Sauve patent. It appears, however, that the Sauve device would be subject to bell tap if installed in a modern telephone system.